bdt500 and Onkyo htx22hd decoding help?

Hi

Im a new owner of the Panasonic bdt500 , Im a little unsure weather I should let the player decode hd formats or my AV reciever (onkyo htx22hd).

Would there be any benefit letting the player decode if its newer?

Also I am planning on just using the main hdmi connection but would It be best using both the main and sub hdmi's , my system is only 3.1 and I dont have a 3d tv so dont need to bypass the amp for video which is what many use the twin connections for. But is there an improvement in PQ/SQ using both?

Many thanks